As mobile devices have been increasingly developed, and the demand for such mobile devices has increased, the demand for batteries has also sharply increased as an energy source for the mobile devices. Accordingly, much research into batteries satisfying various needs has been carried out.
In terms of the shape of batteries, the demand for prismatic secondary batteries or pouch-shaped secondary batteries, which are thin enough to be applied to products, such as mobile phones, is very high. In terms of the material for batteries, on the other hand, the demand for lithium secondary batteries, such as lithium ion batteries and lithium ion polymer batteries, exhibiting high energy density, discharge voltage and power stability, is very high.
Furthermore, secondary batteries may be classified based on the construction of an electrode assembly having a cathode/separator/anode structure. For example, the electrode assembly may be configured to have a jelly-roll (winding) type structure in which long-sheet type cathodes and anodes are wound while separators are disposed respectively between the cathodes and the anodes, a stacking type structure in which pluralities of cathodes and anodes having a predetermined size are sequentially stacked while separators are disposed respectively between the cathodes and the anodes, or a stacking/folding type structure in which pluralities of cathodes and anodes having a predetermined size are sequentially stacked while separators are disposed respectively between the cathodes and the anodes to constitute a bi-cell or a full-cell, and then bi-cells or the full-cells are wound using a separation film.
Recently, much interest has been taken in a pouch-shaped battery configured to have a structure in which such a stacking or stacking/folding type electrode assembly is mounted in a pouch-shaped battery case made of an aluminum laminate sheet because of low manufacturing costs, light weight and easy modification in shape. As a result, the use of pouch-shaped batteries has gradually increased.
FIG. 1 is an exploded perspective view typically illustrating the general structure of a conventional representative pouch-shaped secondary battery.
Referring to FIG. 1,a pouch-shaped battery cell 10 includes an electrode assembly 30, pluralities of electrode tabs 40 and 50 extending from the electrode assembly 30, electrode leads 60 and 70 welded to the electrode tabs 40 and 50, respectively, and a battery case 20 for receiving the electrode assembly 30.
The electrode assembly 30 is a power generating element including cathodes and anodes sequentially stacked while separators are disposed respectively between the cathodes and the anodes. The electrode assembly 30 is configured to have a stacking structure or a stacking/folding structure. The electrode tabs 40 and 50 extend from corresponding electrode plates of the electrode assembly 30. The electrode leads 60 and 70 are electrically connected to the electrode tabs 40 and 50, extending from the corresponding electrode plates of the electrode assembly 30, respectively, for example, by welding. The electrode leads 60 and 70 are partially exposed to the outside of the battery case 20. Also, insulative films 80 to improve sealability between the battery case 20 and the electrode leads 60 and 70 and, at the same time, to secure electrical insulation between the battery case 20 and the electrode leads 60 and 70 are partially attached to the upper and lower surfaces of the electrode leads 60 and 70.
The battery case 20 is made of an aluminum laminate sheet. The battery case 20 has a space defined therein to receive the electrode assembly 30. The battery case 20 is formed generally in the shape of a pouch. In the case that the electrode assembly 30 is a stacking type electrode assembly as shown in FIG. 1, the inner upper end of the battery case 20 is spaced a predetermined distance from the electrode assembly 30 such that the plurality of cathode tabs 40 and the plurality of anode tabs 50 can be coupled to the electrode leads 60 and 70, respectively.
FIG. 2 is a partially enlarged view illustrating the inner upper end of the battery case of the secondary battery shown in FIG. 1, in which the cathode tabs are coupled to each other in a concentrated state and connected to the cathode lead.
Referring to FIG. 2, the plurality of cathode tabs 40, which extend from cathodes 41 of the electrode assembly 30 in a protruding fashion, are connected to one end of the cathode lead 60, for example, in the form of a welded bunch configured by integrally combining the cathode tabs 40 with each other by welding. The cathode lead 60 is sealed by the battery case 20 while the other end 61 of the cathode lead 60, i.e. the end of the cathode lead 60 opposite to the end of the cathode lead 60 to which the welded bunch of the cathode tabs is connected, is exposed to the outside of the battery case 20. Since the plurality of cathode tabs 40 are integrally combined with each other to constitute the welded bunch, the inner upper end of the battery case 20 is spaced a predetermined distance from the upper end surface of the electrode assembly 30, and the cathode tabs 40 combined in the form of the welded bunch are bent approximately in a V shape. Accordingly, the coupling portions between the electrode tabs and the corresponding electrode leads may be referred to as V-form regions.
However, such V-form regions have a problem in terms of battery safety.
Specifically, when the battery drops with the upper end of the battery, i.e. the cathode lead 60 of the battery, facing down, or external physical force is applied to the upper end of the battery, the electrode assembly 30 moves toward the inner upper end of the battery case 20, or the upper end of the battery case 20 is crushed. As a result, anodes of the electrode assembly 30 are brought into contact with the cathode tabs 42 or the cathode lead 61, and therefore, a short circuit may occur inside the battery. Consequently, battery safety is greatly lowered.
Meanwhile, when a pack case of the secondary battery is formed by hot melt resin injection, the upper end of the battery case is pressurized with the result that the V-form region, i.e. the coupling portion between the cathode tabs and the cathode lead, is pushed, and therefore, the V-form region comes into contact with the anode. As a result, a short circuit occurs.
Consequently, there is a high necessity for technology that is capable of fundamentally solving such problems.